So far, all "Chaos Number" monsters, if they are Summoned normally rather than by Chaos Xyz Evolution, require one more material than their normal versions. Also, the first two "Number C" evolutions of non-Over Hundred "Number" require the respective Attribute for their regular Xyz Summons and 1000 Life Points or less in order to activate their effects, while the rest required the "Rank-Up-Magic" cards, "Chaos Field" and "Don Thousand's Throne".

When Summoned without the use of a "Rank-Up" card, they have the same ATK and DEF as their non-Chaos counterparts. When one is Summoned, the Number reverts to its sealed form and enters the Overlay Network. The Overlay Network then explodes, revealing the new sealed form, which then unfolds into the Chaos Number.

In Yu-Gi-Oh! ZEXAL II, Barians Summon Chaos Number through the use of "Rank-Up-Magic" cards. As implied, the Chaos Number Summoned this way is 1 Rank greater than its original form. Also, unlike their non-Barian counterparts, these Chaos Numbers have increased ATK and DEF. Chaos Numbers Summoned this way have a blood-red aura surrounding them, slightly resembling electricity. When someone Summons a Chaos Number by Ranking-Up, they enter a contract with it in order to maintain control of it, at the risk of depleting their life, such as with Girag when he Summoned his "Number C106: Giant Red Hand". It can also put the user at risk in case the Chaos Number is destroyed, which can leave them severely injured, even to the brink of death. If a Chaos Number monster is Summoned via a "Rank-Up-Magic" card (except "Numeron Force", "Astral Force" and "Argent Chaos Force"), "Chaos Field" or "Don Thousand's Throne", their Overlay Units take the form of red diamond-shaped crystals as opposed to glowing orbs, and are referred to as "Chaos Overlay Units", just as with the "CXyz" monsters. The sealed "Barian Gate" appears while doing so.

"Number C" monsters have powerful effects, though this is balanced out by their requirements - needing 1000 or less Life Points for the "Number C" monsters that have the same Rank as their "Number" counterparts, or requiring specific monsters to be attached to them as Xyz Material (or in the Graveyard in the case of Number C101 and Number C103) for Ranked-Up "Number C" monsters.

Chaos Numbers

So far, 18 "Number C" are known to exist, as well as an additional 7 which are "Number C10X".

Chaos imaginary Numbers

While "Chaos Numbers" are generally Summoned by performing Chaos Xyz Evolution on a 'regular' (non-Chaos) "Number", there was a single instance where Don Thousand performed a form of Chaos Xyz Evolution on a monster that was already a "Chaos Number", creating what he called a "Chaos imaginary Number", referencing the mathematical concept of imaginary numbers. Technically, due to this card's name, it is not a true member of the "Number C" archetype.